Voltage control and reactive power management

Voltage control and reactive power management are two facets of an <a href="/facts/Ancillary_service/xcudV9uA">ancillary service</a> that enables reliability of the <a href="/facts/Electric_power_transmission/I9w3lRmM">transmission networks</a> and facilitates the <a href="/facts/Electricity_market/Ufskeaak">electricity market</a> on these networks. Both aspects of this activity are intertwined (voltage change in an <a href="/facts/Alternating_current/qxICS3xa">alternating current</a> (AC) network is effected through production or absorption of <a href="/facts/Reactive_power/EXsaw0B9">reactive power</a>), so within this article the term voltage control will be primarily used to designate this essentially single activity, as suggested by Kirby & Hirst (1997). Voltage control does not include reactive power injections to dampen the <a href="/facts/Grid_oscillation/NQIDnlWM">grid oscillations</a>; these are a part of a separate ancillary service, so-called system stability service. The transmission of reactive power is limited by nature (the typical <a href="/facts/Electrical_reactance/LnvyrUnM">reactance</a> of a <a href="/facts/High-voltage_transmission_line/I9w3lRmM">high-voltage transmission line</a> can be an order of magnitude higher than its <a href="/facts/Electrical_resistance/hxSt0UAj">resistance</a>), so the voltage control is provided through pieces of equipment distributed throughout the power grid, unlike the <a href="/facts/Frequency_control/xcudV9uA">frequency control</a> that is based on maintaining the overall <a href="/facts/Grid_balancing/ACUNKJHh">active power balance</a> in the system.
Generally, an increase in production of reactive power corresponds to higher <a href="/facts/Line_voltage/6VsPewD8">line voltage</a>, while increase of absorption of the reactive power lowers the voltage. In wholesale electricity market, the <a href="/facts/Independent_system_operator/aTlFquQK">independent system operator</a>, together with the owners of transmission lines, define the voltage schedule, a target value or a range of acceptable reference voltages for each generator (typically defined as voltage on the transmission bus). The schedule is typically used as a parameter for the <a href="/facts/Automatic_voltage_control/RWQATaje">automatic voltage control</a>, although sometimes the control is using the target reactive power ("<a href="/facts/MVAR/6R2WrK7b">MVAR</a>") or <a href="/facts/Power_factor/TLKPkptn">power factor</a> as a <a href="/facts/Setpoint_(control_system)/UqfThpJu">setpoint</a>.

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Voltage control and reactive power management